JP3505050B2 - Method for producing polyester film containing fine bubbles - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyester film containing fine bubbles.

[0002]

2. Description of the Related Art Polyester films are widely used as industrial materials because they have various properties in a well-balanced manner and are excellent in cost performance. And, the fine bubble-containing polyester film formed into a film of polyester blended with an incompatible thermoplastic resin,
As a white opaque film that is lightweight and has cushioning properties, it is used in applications such as synthetic paper such as sticker print mounts and magnetic cards. Especially, the cushioning properties of polyester films containing fine bubbles are valued,
It is used as an image-receiving paper or mount (release paper) for products that use images as stickers. As an example of its use, if you select a desired frame or background and pose,
For example, it can be used in so-called amusement machines and the like that can be photographed and processed on the spot to create a facial photograph sticker.

By the way, generally, in the production of a polyester film containing fine bubbles, the film is held by a tenter clip during the transverse stretching. Both end portions of the film winding including the tenter clip gripping portion are generally referred to as ears. This ear film is slit,
It is recycled or scrapped as scrap. It is preferable to recycle the ear film from the viewpoint of raw material cost and in consideration of the environment. However, when the ear film is used as a recycled raw material for the production of the microcellular polyester film, the following problems occur. There is. That is,
The resin that is incompatible with the polyester that was present in the scrap film deteriorates due to the thermal history during the regeneration process, and loses the ability to generate sufficient fine bubbles. Not only that, in this recycled raw material blending system, surprisingly, even the formation of fine bubbles due to the newly added incompatible resin tends to be inhibited. For this reason, in order not to reduce the generation of fine bubbles, the content of the recycled material is limited to an extremely small amount, and most of the ear film has to be discarded.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a polyester film which enables efficient recycling of selvage scraps, can significantly reduce the amount of scraps to be discarded, and is excellent in the state of containing fine bubbles. The task is to do so.

[0005]

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the above-mentioned problems can be easily solved by adopting a manufacturing method having a specific structure. The present invention has been completed. That is, the gist of the present invention is to use polyester A as the central portion,
In the method for producing a polyester film, wherein both ends of the film derived from the polyester B are cut and removed from a film obtained by stretching a sheet coextruded with the polyester B at both ends in at least the transverse direction, the non-phase in the polyester A Content of soluble thermoplastic resin An,
The content Bn of the incompatible thermoplastic resin in the polyester B simultaneously satisfies the following formulas (1) to (5) at the same time.

[0006]

## EQU2 ## 5 ≦ An (% by weight) ≦ 45 0 ≦ Bn (% by weight) ≦ 10 ... An (weight%)> Bn (weight%) + 5 ...

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
In the present invention, the polyester constituting each part of the coextruded sheet is a polyester obtained by using aromatic dicarboxylic acid or its ester and glycol as main starting materials, and 80% or more of repeating structural units are ethylene terephthalate units. Or ethylene-2,6-
Refers to polyesters with naphthalate units. Further, other third component may be contained as long as it does not deviate from the above range.

As the aromatic dicarboxylic acid component constituting the polyester, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p- Oxyethoxybenzoic acid and the like) or two or more thereof can be used. As the glycol component, other than ethylene glycol, for example, diethylene glycol, propylene glycol, butanediol,
One or more of 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used.

In the production method of the present invention, when the sheet is melt-extruded, the polyester B is seen in the width direction of the sheet.
/ Polyester A / polyester B, and the polyester melts are combined and extruded, for example, in or before the T-die. In this case, the polyesters B to be fitted to both ends of the polyester A do not necessarily have to be made of the same raw material, but it is easier to divide the flow path from the one melted by one extruder and supply it to both ends,
Further, it is not necessary to consider the difference in the physical properties in the width direction when performing the stretching in the subsequent step, and therefore it is preferable to use the same raw material.

The microbubble-containing polyester film according to the present invention comprises a polyester containing a thermoplastic resin which is incompatible with the polyester (hereinafter sometimes abbreviated as incompatible resin), stretched in at least one axial direction. It is obtained by doing. The content An of the incompatible resin in the polyester A part is in the range of 5 to 45% by weight, preferably 5 to 35% by weight, and more preferably 10 to 25% by weight based on the total amount with the polyester. When An is less than 5% by weight, the amount of air bubbles formed in the film is too small, so that a film that is sufficiently lightweight and has cushioning properties cannot be manufactured. on the other hand,
If An exceeds 45% by weight, the mechanical strength and thermal stability of the film will be insufficient, and the roughness of the film surface will be too large. Such a film becomes unsuitable for applications such as image-receiving papers which require texture and clear printability. On the other hand, when An exceeds 45% by weight, there may be a problem in productivity such as frequent breakage of the film during stretching.

The density of the film portion derived from polyester A is usually 0.40 to 1.30 g / cm ³ , preferably 0.60 to 1.20 g / cm ³ , and more preferably 0.70 to 1.10 g / cm ³ . The range is cm ³ . Further, in the manufacturing method of the present invention, a certain amount of the ear film is always generated as scrap and is recycled or discarded. That is, both ends of the film winding including the tenter gripping portion in the lateral stretching correspond to this. Here, it is preferable that the ear film is recycled, in view of the advantages of the raw material cost and the environmental consideration of reducing the scrap disposal amount.

In the present invention, the content Bn of the thermoplastic resin which is incompatible with the polyester B is set so that the parts derived from the polyester B, which are the both ends (ears) of the rolled up product, can be recycled. , 0 to 10% by weight, preferably 0 to 3% by weight, and more preferably 0 to 1% by weight. When Bn is more than 10% by weight, there is a problem that the deterioration of the incompatible resin due to heat history becomes remarkable when the film B is regenerated. When this deteriorated recycled raw material is blended in the part B, film breakage frequently occurs during production and the product cannot be collected. In addition, when compounded in the polyester A part, the generation of fine bubbles is hindered by the influence of the deteriorated incompatible resin, and therefore the compounding amount is limited to an extremely small amount.

The density of the film portion derived from polyester B is usually 1.10 g / cm ³ or more, preferably 1.
25 to 1.50 g / cm ³ , more preferably 1.35
The range is from 1.50 g / cm ³ . In the present invention, while An and Bn satisfy the above quantitative relationship,
It is necessary to satisfy the relationship of An> Bn +5. If this relationship is not satisfied, the effect of promoting recycling by reducing the amount of the incompatible resin in the polyester B part becomes unclear.

Specific examples of the thermoplastic resin incompatible with polyester which can be used in the present invention include polyolefins such as polyethylene, polypropylene, polymethylpentene and polymethylbutene, as well as polystyrene, polycarbonate and polyphenylene sulfide. Examples thereof include liquid crystal polyester, and among these, polypropylene, polymethylpentene, and polystyrene are preferable, and polypropylene is more preferable from the viewpoint of cost and productivity. In the following description, polypropylene is a representative thermoplastic resin that is incompatible with polyester.

The above polypropylene is usually 95
A crystalline polypropylene homopolymer having a propylene unit in an amount of not less than mol%, preferably not less than 98 mol% is preferable. In the case of amorphous polypropylene, polypropylene bleeds out on the surface of the non-oriented polyester sheet in the film manufacturing process, and the surface of the cooling drum, the drawing roll, or the like is easily contaminated. In the case of polypropylene in which ethylene units other than propylene units, for example, more than 5 mol% are copolymerized, the production of fine bubbles tends to be insufficient.

The melt flow index (MFI) of the above polypropylene is usually 0.5 to 30 g / 10 minutes,
It is preferably selected from the range of 1.0 to 15 g / 10 minutes. If the MFI is less than 0.5 g / 10 minutes, the bubbles formed tend to become too large and breakage tends to occur during stretching, and if the MFI exceeds 30 g / 10 minutes, the uniformity of the film density over time is uniform. May tend to be inferior and productivity may deteriorate in the production line.

Next, the intrinsic viscosity IVA of the film portion derived from polyester A is preferably 0.45 to 0.70. When the intrinsic viscosity is less than 0.45, film breakage is likely to occur during film formation, and the size of the bubbles becomes non-uniform, making it difficult to control the density, which may reduce productivity. On the other hand, when the intrinsic viscosity exceeds 0.70, the generation of fine bubbles in the film tends to decrease.

The intrinsic viscosity IVB of the film portion derived from polyester B is preferably 0.60 to 0.85. When the intrinsic viscosity is less than 0.60, film breakage tends to occur during film formation. On the other hand, if the intrinsic viscosity exceeds 0.85, the productivity at the time of manufacturing the polyester raw material may decrease. Polyester A and B
Difference in intrinsic viscosity of derived film part (IVB-IVA)
Is preferably 0 to 0.15. When the difference is negative, the film tends to be broken near the clip gripping portion. On the other hand, when the difference exceeds 0.15, film breakage from the A / B interface tends to occur.

In the production method of the present invention, the density, cushioning property and surface roughness of the film containing fine bubbles are adjusted by controlling the size of the dispersed particle size of polypropylene formed in the melt extrusion step. You can In order to make the dispersed particle size within a desired range, it is preferable to include a surfactant in the polyester. Examples of the above-mentioned surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and the like. Among these, nonionic surfactants, particularly silicones. A system surfactant and polyalkylene glycol are preferable. Examples of the silicone-based surfactant include an organopolysiloxane-polyoxyalkylene copolymer and an alkenylsiloxane having a polyoxyalkylene side chain. Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, copolymers of ethylene glycol and propylene glycol, and the like. The content of the surfactant in the total raw material for forming the layer A is usually 0.005 to
It is set to 2.0% by weight, preferably 0.01 to 1.0% by weight. When the content of the surfactant is more than 2.0% by weight, the effect of the surfactant is not improved anymore, and troubles in the extruder or deterioration of the polyester may occur. On the other hand, the content of surfactant is 0.0
If it is less than 05% by weight, the effect may be insufficiently expressed.

The film obtained by the production method of the present invention contains titanium dioxide in order to impart whiteness and hiding power.
Barium sulfate and other known white pigments may be added. Furthermore, in order to further increase the whiteness, it is also effective to add a fluorescent whitening agent. It is preferable to add the white pigment and the fluorescent whitening agent only to the polyester A part from the viewpoint of raw material cost.

Two or more kinds of white pigments can be contained, but in that case, it is preferable to contain at least titanium dioxide or barium sulfate. Polyester A
The content of the white pigment in the parts is preferably 0.5 to 20% by weight, and more preferably 1.0 to 15% by weight. Examples of fluorescent whitening agents that can be suitably used include "Ubitech", a product manufactured by Ciba-Geigy, and "OB-1", a product manufactured by Eastman. The preferred content of the optical brightening agent in the polyester A part is in the range of 0 to 0.30% by weight.

In the present invention, in addition to the above white pigment and fluorescent whitening agent, known antioxidants, heat stabilizers, lubricants, antistatic agents, dyes may be added to polyester or polypropylene, if necessary. Additives such as pigments can be added. A method of extruding a melt composed of at least a polyester A part and a polyester B part so that the B parts are at both ends when seen in the width direction of the sheet as described above is conventionally known, for example, Japanese Patent Laid-Open No. 55-
No. 118832, JP-A-1-118428,
The alignment method disclosed in Japanese Patent Laid-Open No. 8-207119 can be applied.

After the polymer melts have been previously combined and coextruded by these methods, stretching is performed by a tenter method at least in the transverse direction. However, a biaxial stretching method and a heat treatment method are usually used in combination in order to form fine bubbles satisfactorily and to appropriately satisfy the strength and dimensional stability of the film. Hereinafter, an example of using biaxial stretching in the manufacturing method of the present invention will be described in detail. First, the raw materials of the composition for each part in the width direction are supplied to the extruder corresponding to each part of the coextrusion extruder. That is, the raw material resin is usually charged into two or three extruders, melted and kneaded for each extruder line, and then guided to a multi-manifold or a feed block for guiding a melt flow of 3 parts to form a molten sheet from a die. Push out.

Specifically, in order to make the constitution of each part B / A / B when viewed in the width direction of the sheet, each raw material forming part A and part B is extruded from one extruder to form layer B. A method of dividing the melt line on the way is generally used. A quantitative feeder such as a gear pump is installed in the melt line after the division, and the flow rate of the polymer melt in the B part, which is aligned with both ends of the A part, is adjusted to control the width of the B part. Of course, it is also effective to install a quantitative feeder on the melt line of the A part polyester in order to adjust the width and the thickness of the A part. Next, the molten sheet extruded from the die is rapidly cooled and solidified on the rotating cooling drum to a temperature not higher than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness and cooling effect of the sheet, it is preferable to increase the adhesion between the sheet and the rotating cooling drum, and in the present invention, the electrostatic application adhesion method and / or the liquid coating adhesion method is preferable. Adopted.

Next, the obtained sheet is biaxially stretched to form a film. In the production method of the present invention, the fine bubbles in the film portion derived from polyester A are generated by such stretching. First, a stretching temperature of usually 70 to 150 ° C, preferably 75 to 130 ° C, usually 2.5 to 6
The unstretched sheet is stretched in one direction (longitudinal direction) under the condition of a draw ratio of 3 times, preferably 3.0 to 5 times. A roll and tenter type stretching machine can be used for such stretching. Then usually 75 to 150 ° C., preferably 8
A biaxially oriented film is obtained by stretching in a direction (transverse direction) orthogonal to the first stage under the conditions of a stretching temperature of 0 to 140 ° C. and usually a stretching ratio of 2.5 to 6 times, preferably 3.0 to 5 times. obtain.
For such stretching, a tenter type stretching machine can be used.

A method in which the above-mentioned unidirectional stretching is performed in two or more steps can also be adopted, but in that case also, it is preferable that the final stretching ratio falls within the above range. Further, it is possible to simultaneously biaxially stretch the unstretched sheet so that the area ratio becomes 7 to 30 times. Heat treatment is 150 ~
It is carried out at 250 ° C. for 1 second to 5 minutes under 30% elongation, limited shrinkage or constant length. After biaxial stretching, 110 ° C to 1
A method of re-stretching 1.05 to 2.0 times in the machine direction at a temperature of 80 ° C. and then heat-treating may also be employed. At this time, a method such as heat setting before re-longitudinal stretching, longitudinal relaxation after re-longitudinal stretching, or before or after re-longitudinal stretching and longitudinal micro-stretching can be appropriately adopted.
Further, re-stretching may be performed in the transverse direction as well. In addition, various surface treatments may be performed in the film forming process as needed.

The microbubble-containing polyester film produced by the production method of the present invention is not always a single layer. When the polyester A part is composed of a plurality of layers, at least one of the layers may be a fine bubble-containing layer containing an incompatible thermoplastic resin. The thickness of the fine bubble-containing polyester film is usually 20 to 250 μm,
It is preferably in the range of 50 to 200 μm. Further, by making the best use of its characteristics, it is preferably used for printer image receiving paper, sticker print mount, label, recording paper, poster, lithographic printing plate, packaging material, sticky note and the like.

[0028]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The evaluation methods in Examples and Comparative Examples are as follows. Further, all "parts" in the component ratios in Examples and Comparative Examples mean "parts by weight", and the silicone-based surfactant is "SH193" manufactured by Toray Silicone Co., Ltd. (1) Intrinsic viscosity of polyester [η] (dl / g) Phenol / tetrachloroethane: 50/50 (weight ratio) is mixed with 1 g of polyester in which other polymer components incompatible with polyester and white pigment are removed. The solvent was added at a ratio of 100 ml to dissolve the solvent, and the temperature was measured at 30 ° C. (2) Melt flow index M ・ F ・ I
(G / 10min) It measured according to JIS K-6758-1981. The higher this value, the lower the melt viscosity of the polymer.

Example 1 A polyethylene terephthalate chip having an intrinsic viscosity of 0.69, 13% by weight of a crystalline polypropylene chip having M · F · I of 10 g / 10 min, 2.4% by weight of titanium oxide, and a silicone-based surface active agent. After blending 0.1% by weight of the agent, polyester raw material X was prepared by blending uniformly. Raw material Y was prepared by separately adjusting a polyethylene terephthalate chip having an intrinsic viscosity of 0.66.

Each of the above raw materials was put into a separate extruder and melted at 280 ° C., and each of the obtained melts was introduced into a T-die to form a raw material Y / raw material X / raw material Y in the width direction. I joined them in advance. The length ratio of the sheet in each part in the width direction was set to 1: 8: 1. It was extruded in a slit shape by transverse coextrusion and cooled on a cast roll at 30 ° C. to obtain an unoriented sheet. And the film flow direction (vertical direction)
Roll-stretched at 85 ° C for 3.4 times, and then transversely stretched at 110 ° C for 3.1 times by tenter, and further heat-treated at 230 ° C for 5 seconds in the tenter stretching machine to finally obtain the raw material X. A biaxially oriented film containing fine bubbles in the origin was obtained. The product obtained by slitting the portion of the film derived from the raw material Y and subjecting it to a regeneration treatment could be suitably used as the material of the raw material Y again.

Example 2 In Example 1, when each raw material was melted by a separate extruder and extruded from the T-die, raw material Y / (raw material X and raw material Y were laminated in the order of YXY in the thickness direction). (Region) / raw material Y were combined in advance. In addition, the width direction length ratio of the sheet of each part was 1: 8: 1, and the flow rate of the melt of the raw material X and the raw material Y was 14: 1 in the central laminated region. Thereafter, in the same manner as in Example 1, a biaxially oriented laminated film containing fine bubbles was obtained. The product obtained by slitting the portion of the film derived from the raw material Y and subjecting it to a regeneration treatment could be suitably used as the material of the raw material Y again.

Comparative Example 1 The raw material X of Example 1 was melted and extruded from the T-die with a single structure in the width direction, and then a biaxially oriented film containing fine bubbles was obtained in the same manner as in Example 1. When scraps obtained by slitting the ears of the obtained film were recycled and the whole amount thereof was mixed in the raw material X, the result was that the generation of fine bubbles after forming into a film was reduced. In order to maintain the production amount of fine bubbles, the recycling of scrap was practically impossible, and therefore the raw material yield was poor.

Example 3 In the same manner as in Example 1, except that the intrinsic viscosity of the polyethylene terephthalate chips used as the raw material X was 0.74 and the intrinsic viscosity of the polyethylene terephthalate chips used as the raw material Y was 0.64. A biaxially oriented film containing fine bubbles was obtained. At the time of production, film breakage sporadically occurred near the tenter clip gripping portion, and the processing yield was slightly inferior to that of Example 1.

Example 4 In the same manner as in Example 1, except that the intrinsic viscosity of the polyethylene terephthalate chips used as the raw material X was 0.74 and the intrinsic viscosity of the polyethylene terephthalate chips used as the raw material Y was 0.84. A biaxially oriented film containing fine bubbles was obtained. At the time of production, film breakage occurred near the interface between the raw material X and the raw material Y, and the processing yield was slightly inferior to that of Example 1. The results obtained above are summarized in Table 1 below.

[0035]

[Table 1]

[0036]

[Effects of the Invention] Conventionally, the scraps of the ears generated in the manufacturing process of the polyester film containing fine air bubbles are discarded because the incompatible thermoplastic resin in the scrap is deteriorated due to the heat history during the recycling process. It had to be discharged due to the treatment. However, by applying the manufacturing method of the present invention, it is possible to efficiently recycle the scraps in the ears, and at the same time, it is possible to significantly reduce the amount of scraps to be discarded.
Considering the merits in terms of production cost and the positive impact on the environment, its industrial value is extremely high.

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Claims (3)

(57) [Claims] 1. A polyester film obtained by cutting and removing both end portions of a film derived from the polyester B from a film obtained by stretching a sheet coextruded with the polyester A at the center portion and the polyester B at both end portions in the transverse direction. In the production method of the above, the content An of the incompatible thermoplastic resin in the polyester A and the content Bn of the incompatible thermoplastic resin in the polyester B simultaneously satisfy the following expressions (1) to (5). A method for producing a polyester film containing fine bubbles. ## EQU1 ## 5 ≦ An (wt%) ≦ 45 ... 0 ≦ Bn (wt%) ≦ 10 ... An (wt%)> Bn (wt%) + 5 2. The intrinsic viscosity IVA of the film portion derived from the polyester A is 0.45 to 0.70, and the intrinsic viscosity IVB of both end portions of the film derived from the polyester B is 0.
60-0.85, and IVB-IVA is 0-0.
15. The method for producing a microbubble-containing polyester film according to claim 1, wherein the number is 15. 3. The method for producing a fine bubble-containing polyester film according to claim 1, wherein the incompatible thermoplastic resin is at least one selected from polypropylene, polymethylpentene and polystyrene.